Question

Sin(a-30)-sin(a+30)=-coss​

Answer 1

We know that:

Sin(a + b) = sin(a)*cos(b) + sin(b)*cos(a)

Then if we use this property in our expression:

sin(a-30)-sin(a+30)

We get:

sin(a)*cos(-30°) + sin(-30°)*cos(a) - sin(a)*cos(30°) - sin(30°)*cos(a)

Now remember that:

sin(-x) = -sin(x)

and

cos(-x) = cos(x)

Then we can rewrite our expression as:

sin(a)*cos(30°) - sin(30°)*cos(a) - sin(a)*cos(30°) - sin(30°)*cos(a)

= -2*sin(30°)*cos(a)

and sin(30°) = 0.5

Then:

-2*sin(30°)*cos(a) = -2*0.5*cos(a) = -cos(a)

So we get:

sin(a-30)-sin(a+30)= - cos(a)